Molded plastic battery container

ABSTRACT

A battery container made of molded plastic and preferably formed in a single unitary structure. The container comprises a generally rectangular hollow container with a plurality of internal partitions formed as integral parts of the container bottom and side walls dividing the interior space into a plurality of battery cells. A plurality of ribs are formed on the mold surface that forms the bottom of the container, the ribs being in alignment with the cavities between adjacent mold cores and forming a plurality of parallel grooves in the lower surface of the container bottom. The ribs are at least as wide as the width of the cavities between adjacent cores at the top of the container so that the upper ends of the partitions formed in said cavities fit into the resulting grooves formed by the ribs when the containers are stacked on top of each other. The mold gates are formed in the centers of the ribs, and the feed nozzles extend all the way through the ribs to avoid any reduction in the groove depth due to buildup of plastic at the gates. To maintain a substantially uniform thickness in the bottom of the container in the gate regions, the corners of the mold cores are provided with recesses adjacent the gate regions, thereby increasing the thickness of the lower ends of the partitions in those regions.

This is a division of application Ser. No. 551,295 filed Feb. 20, 1975now U.S. Pat. No. 3,995,008.

DESCRIPTION OF THE INVENTION

The present invention relates generally to molded plastic batterycontainers, particularly for automotive batteries, and to methods andapparatus for the molding of such containers.

Battery containers made of molded plastic generally have internalpartitions formed as integral parts of the bottom and side walls of thecontainer and extending all the way to the top of the container toprevent the leakage of liquid between adjacent cells. These containersare usually formed as unitary structures in a single molding operation,with a plurality of mold cores defining the internal cavities which formthe partitions. The mold is usually gated at the center of the lower endof each partition-forming cavity and the parallel end walls of thecontainer.

One of the problems encountered with containers of this type is that thepartitions become distorted or warped during handling and storage,particularly when the containers are stacked on top of each other.Another problem is that defective partitions may be produced due todifferences in the feed rates at adjacent gates in the mold used to formthe container. These differential feed rates inevitably occur incommercial production, particularly when the temperatures at the variousgates are independently controlled by separate electrical heatingelements. It is difficult to maintain equal temperatures at all thegates in any given mold, primarily because of the independentlycontrolled heating elements. When the plastic is fed through a pair ofadjacent gates at different flow rates, the pressure of the moltenplastic increases faster on one side of the corresponding mold coresthan on the other side. When the mold cores are supported at only oneend, this pressure differential across one of the cores displaces thatcore toward the lower pressure cavity, thereby making one partition toothin and the adjacent partition too thick. The thinner partitions, ofcourse, are more susceptible to cold shorts and voids or incompletewelds resulting in fluid leakage between adjacent battery cells andconsequent failure of the battery.

It is a primary object of the present invention to provide an improvedmolded plastic battery container which prevents distortion of theinternal partitions when the containers are stacked on top of eachother.

It is another object of the invention to provide such an improved moldedplastic battery container which can be molded with a more uniformthickness in the internal partitions, and a more uniform density ofplastic throughout the partitions. In this connection, a related objectof the invention is to provide such an improved battery container whichgreatly reduces the possibility of battery failure due to defectivepartitions causing fluid leakage between adjacent cells in the battery.

A further object of the invention is to provide an improved method andapparatus for molding plastic battery containers with partitions ofuniform thickness. A more specific object is to provide such an improvedmolding method and apparatus which avoid displacement of the mold coresdue to unequal plastic feed rates at adjacent gates in the mold.

Other objects and advantages of the invention will be apparent from thefollowing detailed description and the accompanying drawings, in which:

FIG. 1 is a bottom perspective view of a molded plastic batterycontainer embodying the invention;

FIG. 2 is an enlarged section taken along line 2--2 in FIG. 1; and

FIG. 3 is an enlarged fragmentary section illustrating the molding of abottom portion of the container shown in FIG. 1.

While the invention will be described in connection with a certainpreferred embodiment, it will be understood that it is not intended tolimit the invention to that particular embodiment. On the contrary, itis intended to cover all alternatives, modifications, and equivalents asmay be included within the spirit and scope of the invention as definedby the appended claims.

Turning now to the drawings and referring first to FIG. 1, there isshown a generally rectangular battery container 10 made of moldedplastic. Although the top of the container is closed by application of alid during assembly of the battery, the container 10 is initially formedwith a completely open top. The container includes a plurality ofinternal partitions 11 extending parallel to the end walls 12 and 13 ofthe container to form a plurality of battery cells 14. The entirecontainer is molded in one piece, including the partitions 11 which areformed as integral parts of the bottom wall 15 and the side walls 16 and17 of the container. These partitions 11 extend all the way to the topedge of the container to prevent liquid spillover between adjacent cells14. As illustrated in FIG. 3, the cells 14 are defined by a plurality ofmold cores 18 positioned at equal spaces within the mold shell thatforms the external walls 12-13 and 15-17 during the molding operation.The molten plastic is normally introduced into the mold assembly througha plurality of gates 19 aligned with the partition-forming cavitiesbetween the mold cores 18 and with the cavities that form the end walls12 and 13. These gates 19 are shown at the top of the mold assembly inFIG. 3, but this is actually the bottom of the container 10 since it isshown molded in the inverted position.

In accordance with one important aspect of the present invention, theexterior surface of the container bottom forms a plurality of parallelgrooves aligned with the internal partitions, the grooves being at leastas wide as the upper ends of the partitions so that the partitions ofone container nest with the grooves in the bottom of another containerwhen they are stacked on top of each other. Thus, in the illustrativeembodiment the bottom wall 15 of the container 10 forms a plurality ofgrooves 20 aligned with the partitions 11 and extending parallel to theend walls 12 and 13. Each groove 20 is slightly wider than the upper endof one of the partitions 11 so that when two or more containers arestacked on top of one another, as illustrated in FIG. 2, the upper endsof the partitions 11 fit into the grooves 20. Consequently, thepartitions 11 are positively held in their original positions, parallelto the end walls 12 and 13, preventing distortion and warpage of thepartitions due to the forces that are often exerted thereon duringhandling and storage.

To permit the partitions 11 to nest with the grooves 20, the lowerportion of the container 10 is tapered inwardly so that the bottom ofone container nests within the open top of a similar container whenstacked thereon. Thus, the end walls 12 and 13 and the side walls 16 and17 of the container 10 taper inwardly at a slight angle so that the areaof the container bottom is slightly smaller than the open area at thetop of the container, thereby permitting the bottom of the container tonest within the open top of a similar container as shown in FIG. 2. Tofurther facilitate this nesting of the stacked containers, the peripheryof the bottom of the container is also rounded, as at 15a in FIG. 2, sothat the external surface of the bottom wall 15 of the container is madeeven smaller to more readily fit within the open top of a similarcontainer.

In order to form the grooves 20, the mold surface 21 that forms thebottom of the container includes a plurality of ribs 22 in alignmentwith the partition-forming cavities 23 between adjacent mold cores 18.These ribs 22 form the grooves 20 in the desired location, i.e., inalignment with the bases of the partitions 11 formed within the cavities23. As can be seen in FIG. 3, the ribs 22 also form a reduced throat 24between the surface of each rib and the free end of each mold core 18.These reduced throats 24 have been found to be particularly valuable inproducing more uniform partitions, apparently by reducing lateraldisplacement of the mold cores 18 due to differences in the rates atwhich molten plastic is fed through adjacent gates 19. Thesedifferential feed rates inevitably occur in commercial production,particularly when the temperatures at the various gates areindependently controlled by separate electrical heating elements. It isdifficult to maintain equal temperatures at all the gates in any givenmold, primarily because of the independently controlled heatingelements.

When the plastic was fed through a pair of adjacent gates at differentflow rates in prior molding techniques, the pressure would increasefaster on one side of the corresponding mold core than on the otherside. Since the mold cores are unsupported at the ends closest to thegates, this pressure differential across one of the cores would displacethat core toward the lower pressure side, thereby making the partitionon one side of the core too thin and the partition on the other side toothick. The thinner partitions, of course, were also weaker and moresusceptible to cold shorts and voids or incomplete welds, resulting influid leakage between adjacent battery cells and consequent failure ofthe battery.

With the improved design provided by this invention, different feedrates tend to automatically vary the mold volumes being fed by therespective gates so that substantially equal pressures are maintainedthroughout the mold, thereby preventing lateral displacement of the moldcores. For example, if the feed rate at gate 19 in FIG. 3 is greaterthan the feed rate at the adjacent gate 19, the plastic entering themold from the higher flow rate gate 19 will produce a "wave front"closer to the lower feed rate gate 19' than the gate 19, as indicated at25 in FIG. 3. As a result, a greater percentage of the plastic enteringthrough the gate 19' feeds into the cavity 23', while a greaterpercentage of the plastic entering through the gate 19 feeds into thecavities which form the bottom wall 15 of the container. Consequently, asubstantially equal pressure of molten plastic is maintained on bothsides of the mold core 18, in spite of the differential feed ratesthrough the two adjacent gates 19 and 19'.

In accordance with another aspect of this invention, the feed nozzles atthe mold gates 19 extend into the mold beyond the innermost surfaces ofthe ribs 22 to ensure against any reduction in the groove depths due toplastic buildup at the gate locations. Thus, in the illustrativeembodiment the feed nozzles 30 extend completely through the ribs 22 sothat even if there is a slight buildup of plastic at the end of thegate, the surface of this plastic buildup will still be below the levelof the groove in which that gate is located. To avoid any restriction inthe throats 24 between the ribs 22 and the mold cores 18 in the gateareas occupied by the nozzles 30, the adjacent corners of the mold coresare provided with recesses 31 complementary to the shape of the nozzletips so that the space between the nozzle 30 and the recesses 31 hassubstantially the same width as the space between the ribs 22 and thecorners of the mold cores 18. Consequently, there is even distributionof plastic across the entire width of the container, including the areasimmediately adjacent the various gates 19. In the final product, theresult is a depression 32 in the exterior surface of the bottom wall 15at each gate location, and an increase in the thickness of the adjacentportions 33 of the bases of the partitions 11 (FIG. 2).

As can be seen from the foregoing detailed description, this inventionprovides an improved battery container which prevents distortion of theinternal partitions when the containers are stacked on top of eachother, due to the nesting of the grooved bottom surfaces of the uppercontainers with the top ends of the partitions and end walls of thelower partitions. Furthermore, the same ribs which form the bottomgrooves also improve the flow characteristics of molten plastic withinthe mold during the molding operation, producing partitions with a moreuniform thickness and density. The reduced throats formed between theribs and the adjacent mold cores apparently reduce displacement of themold cores due to different feed rates at adjacent gates in the moldwall which forms the bottom of the container. Consequently, theresulting battery container greatly reduces the possibility of batteryfailure due to defective partitions due to cold shorts and voids orincomplete welds resulting in fluid leakage between adjacent batterycells. Another major effect of the ribbed bottoms is a reduction of theincidence of partition warpage, which condition precipitates problems insubsequent manufacturing operations, notably the inability to effect agood cover seal along the line of a warped partition, resulting inleakage potential from adjacent cells.

I claim as my invention:
 1. A molded plastic battery containercomprisinga generally rectangular hollow container with a closed bottomand open top, a plurality of vertical partitions formed as integralparts of the container bottom and side walls and extending upwardly tothe top of the container to divide the container into separate cells,the external surface of the container bottom forming a plurality ofgrooves aligned with said partitions, the width of the grooves being atleast as wide as the thickness of the top ends of the partitions so thatmultiple containers nest together when stacked on top of each other withthe top ends of the partitions of one container fitting into the bottomgrooves of another container, a depression formed in the center of eachgroove due to the seating of feed nozzles therein during the molding ofthe container, the depression being at least as deep as the groove andthe thicknesses of said said partition being increased in the regions ofsaid depression at the lower ends thereof to provide a substantiallyuniform bottom wall thickness.
 2. A molded plastic battery containercomprisinga generally rectangular hollow container with a closed bottomand open top, a plurality of vertical partitions formed as integralparts of the container bottom and side walls and extending upwardly tothe top of the container to divide the container into separate cells,the external surface of the container bottom forming a plurality ofgrooves aligned with said partitions, the width of the grooves being atleast as wide as the thickness of the top ends of the partitions so thatmultiple containers nest together when stacked on top of each other withthe top ends of the partitions of one container fitting into the bottomgrooves of another container, the container wall between the tops ofsaid grooves and the bottoms of said cells being thinner than theadjacent portions of said partitions and the remainder of the bottomwall of the container.